As a kind of a plasma processing of a target object by using a plasma processing apparatus, there is a plasma etching. A resist mask used in the plasma etching is formed by a photolithography technique, and a limit size of a pattern formed on an etching target layer depends on a resolution of the resist mask formed by the photolithography technique. There is, however, a limit in the resolution of the resist mask (that is, a resolution limit). As a demand for high integration of electronic devices is getting higher, it is required to form a pattern smaller than the resolution limit of the resist mask. For this reason, as described in Patent Document 1, there is proposed a technique of adjusting a size of the resist mask and reducing a width of an opening of the resist mask by forming a silicon oxide film on the resist mask.    Patent Document 1: Japanese Patent Laid-open Publication No. 2004-080033
Meanwhile, as the electronic devices are miniaturized to meet the recent trend of the high integration, it is required to control a critical dimension (CD) with high accuracy when forming the pattern on the target object, particularly, when performing the etching on an organic film or the like included in a multilayered structure. In such a case, though a silicon-containing antireflection film formed on the organic film is used as a mask for the etching of the organic film, there may be a trade-off relationship between a removal of the mask formed from the antireflection film and an influence upon a sidewall shape of the organic film. In this regard, there has been a demand for a technique capable of reducing the influence of the removal of the mask for use in the etching of the organic film upon the sidewall shape of the organic film.